1. Field of the Invention
The present invention relates to absorbent structures suitable for use in absorbent products. Specifically, the present invention relates to an absorbent structure having a dual Z-direction gradient.
2. Description of the Related Art
Absorbent structures suitable for use in absorbent products are known. Typically, such absorbent structures comprise an absorbent fibrous matrix such as a batt of comminuted wood pulp fluff. In order to enhance the absorbent capacity of such absorbent structures, it is common to incorporate into them a high-absorbency material known as a superabsorbent material. Such high-absorbency materials are generally capable of absorbing at least about 10, preferably about 15, and most preferably at least about 20 and up to 100 times their weight in water.
In order to enhance the fluid handling capability of absorbent structures formed from a wood pulp fluff matrix, it is known to provide the wood pulp fluff matrix with a Z-direction density gradient. Reference to a Z-direction refers to the thickness of a given fibrous matrix. That is, a fibrous matrix generally comprises first and second opposed major planar surfaces. The first and second opposed major planar surfaces define the length and width (X and Y direction) of the fibrous matrix. The Z-direction refers to the distance separating the first and second major planar surfaces (thickness).
For example, U.S. Pat. No. 5,009,650 issued Apr. 23, 1991, to Bernardin describes an absorbent structure having a fibrous upper layer and a fibrous lower layer. The upper layer has a density of from about 0.03 to about 0.14 gram per cubic centimeter, and the lower layer has a density of from about 0.14 to about 0.3 gram per cubic centimeter. Thus, it is seen that Bernardin describes a fibrous matrix comprising an upper and a lower layer wherein there is a density gradient in the fibrous matrix defined by the low density upper layer and the high density lower layer. Such a structure is said to be well suited for quickly absorbing a liquid discharged on the upper layer and transferring the liquid to a lower layer where the liquid is transported away from the point of discharge.
Similarly, U.S. Pat. No. 4,699,823 issued Oct. 13, 1987, to Kellenberger et al. describes a nonlayered absorbent structure having a Z-directional superabsorbent concentration gradient. Kellenberger describes a fibrous matrix of wood pulp fluff containing superabsorbent particles disposed therein. The concentration of superabsorbent particles dispersed within the fibrous matrix is said to increase from one planar surface of the fibrous matrix to the opposite planar surface. This arrangement of superabsorbent material is said to prevent gel blocking when the planar surface, having a relatively low concentration of superabsorbent particles, is positioned nearest the body of a wearer.
While both density gradients and superabsorbent gradients are known in the art and have proven effective in improving the performance of absorbent products, it is desired to further optimize absorbent structures suited for use in absorbent products.